Permeability of the labyrinthine windows in guinea pigs

Permeability of the labyrinthine windows in guinea pigs was investigated by electron microscopy using horseradish peroxidase (HRP). In the round window membrane, HRP particles were readily taken up by the epithelial cells and were transported to the subepithelial layer which was regarded as being bathed in the perilymph. The oval window also appears to allow the passage of the macromolecules in view of the HRP-labeled granules in the chondrocytes of the stapediovestibular joint. The transport of the HRP particles from the middle ear to the inner ear was confirmed by the uptake of those in the saccular epithelium after 30--40 min exposure to the tracer.